diff --git a/runbot_merge/models/pull_requests.py b/runbot_merge/models/pull_requests.py
index 8f7e0181..a8f10cd4 100644
--- a/runbot_merge/models/pull_requests.py
+++ b/runbot_merge/models/pull_requests.py
@@ -369,6 +369,7 @@ class PullRequests(models.Model):
     )
     message = fields.Text(required=True)
     squash = fields.Boolean(default=False)
+    rebase = fields.Boolean(default=True)
 
     delegates = fields.Many2many('res.partner', help="Delegate reviewers, not intrinsically reviewers but can review this PR")
     priority = fields.Selection([
@@ -440,6 +441,8 @@ class PullRequests(models.Model):
         elif name in ('p', 'priority'):
             if param in ('0', '1', '2'):
                 return ('priority', int(param))
+        elif name == 'rebase':
+            return ('rebase', flag != '-')
 
         return None
 
@@ -459,6 +462,9 @@ class PullRequests(models.Model):
         p(riority)=2|1|0
           sets the priority to normal (2), pressing (1) or urgent (0).
           Lower-priority PRs are selected first and batched together.
+        rebase+/-
+          Whether the PR should be rebased-and-merged (the default) or just
+          merged normally.
         """
         assert self, "parsing commands must be executed in an actual PR"
 
@@ -530,6 +536,9 @@ class PullRequests(models.Model):
                             self.repository.name, self.number,
                             author.github_login, self.target.name,
                         )
+            elif command == 'rebase':
+                # anyone can rebase- their PR I guess?
+                self.rebase = param
 
             _logger.info(
                 "%s %s(%s) on %s:%s by %s (%s)",
@@ -889,19 +898,52 @@ class Batch(models.Model):
                 pr.repository.name, pr.number, pr.target.name, pr.squash
             )
 
+            target = 'tmp.{}'.format(pr.target.name)
+            suffix = '\n\ncloses {pr.repository.name}#{pr.number}'.format(pr=pr)
             try:
-                # FIXME: !rebase
-
-                target = 'tmp.{}'.format(pr.target.name)
-                suffix = '\n\ncloses {pr.repository.name}#{pr.number}'.format(pr=pr)
+                # nb: pr_commits is oldest to newest so pr.head is pr_commits[-1]
                 pr_commits = gh.commits(pr.number)
-                if len(pr_commits) == 1:
+                rebase_and_merge = pr.rebase
+                squash = rebase_and_merge and len(pr_commits) == 1
+                if squash:
                     pr_commits[0]['commit']['message'] += suffix
                     new_heads[pr] = gh.rebase(pr.number, target, commits=pr_commits)
-                else:
+                elif rebase_and_merge:
                     msg = pr.message + suffix
                     h = gh.rebase(pr.number, target, reset=True, commits=pr_commits)
                     new_heads[pr] = gh.merge(h, target, msg)['sha']
+                else:
+                    pr_head = pr_commits[-1] # pr_commits is oldest to newest
+                    base_commit = None
+                    head_parents = {p['sha'] for p in pr_head['parents']}
+                    if len(head_parents) > 1:
+                        # look for parent(s?) of pr_head not in PR, means it's
+                        # from target (so we merged target in pr)
+                        merge = head_parents - {c['sha'] for c in pr_commits}
+                        assert len(merge) <= 1, \
+                            ">1 parent from base in PR's head is not supported"
+                        if len(merge) == 1:
+                            [base_commit] = merge
+
+                    if base_commit:
+                        # replicate pr_head with base_commit replaced by
+                        # the current head
+                        original_head = gh.head(target)
+                        merge_tree = gh.merge(pr_head['sha'], target, 'temp merge')['tree']['sha']
+                        new_parents = [original_head] + list(head_parents - {base_commit})
+                        copy = gh('post', 'git/commits', json={
+                            'message': pr_head['commit']['message'] + suffix,
+                            'tree': merge_tree,
+                            'author': pr_head['commit']['author'],
+                            'committer': pr_head['commit']['committer'],
+                            'parents': new_parents,
+                        }).json()
+                        gh.set_ref(target, copy['sha'])
+                        new_heads[pr] = copy['sha']
+                    else:
+                        # otherwise do a regular merge
+                        msg = pr.message + suffix
+                        new_heads[pr] = gh.merge(pr.head, target, msg)['sha']
             except (exceptions.MergeError, AssertionError) as e:
                 _logger.exception("Failed to merge %s:%s into staging branch (error: %s)", pr.repository.name, pr.number, e)
                 pr.state = 'error'
diff --git a/runbot_merge/tests/fake_github/__init__.py b/runbot_merge/tests/fake_github/__init__.py
index 69fcbdfe..2faf54cf 100644
--- a/runbot_merge/tests/fake_github/__init__.py
+++ b/runbot_merge/tests/fake_github/__init__.py
@@ -138,25 +138,19 @@ class Repo(object):
         c.statuses.append((status, context, description))
         self.notify('status', self.name, context, status, c.id)
 
-    def make_commit(self, ref, message, author, committer=None, tree=None, changes=None):
-        assert (tree is None) ^ (changes is None), \
-            "a commit must provide either a full tree or changes to the previous tree"
+    def make_commit(self, ref, message, author, committer=None, tree=None):
+        assert tree, "a commit must provide either a full tree"
 
-        branch = False
-        if ref is None:
-            pids = []
-        else:
-            pid = ref
-            if not re.match(r'[0-9a-f]{40}', ref):
-                pid = self.refs[ref]
-                branch = True
-            parent = self.objects[pid]
-            pids = [pid]
+        refs = ref or []
+        if not isinstance(refs, list):
+            refs = [ref]
 
-        if tree is None:
-            # TODO?
-            tid = self._update_tree(parent.tree, changes)
-        elif type(tree) is type(u''):
+        pids = [
+            ref if re.match(r'[0-9a-f]{40}', ref) else self.refs[ref]
+            for ref in refs
+        ]
+
+        if type(tree) is type(u''):
             assert isinstance(self.objects.get(tree), dict)
             tid = tree
         else:
@@ -164,8 +158,8 @@ class Repo(object):
 
         c = Commit(tid, message, author, committer or author, parents=pids)
         self.objects[c.id] = c
-        if branch:
-            self.refs[ref] = c.id
+        if refs and refs[0] != pids[0]:
+            self.refs[refs[0]] = c.id
         return c.id
 
     def _save_tree(self, t):
@@ -268,11 +262,10 @@ class Repo(object):
 
     def _create_commit(self, r):
         body = json.loads(r.body)
-        [parent] = body.get('parents') or [None]
         author = body.get('author') or {'name': 'default', 'email': 'default', 'date': 'Z'}
         try:
             sha = self.make_commit(
-                ref=parent,
+                ref=(body.get('parents')),
                 message=body['message'],
                 author=author,
                 committer=body.get('committer') or author,
diff --git a/runbot_merge/tests/remote.py b/runbot_merge/tests/remote.py
index ddc1efbd..9e4db608 100644
--- a/runbot_merge/tests/remote.py
+++ b/runbot_merge/tests/remote.py
@@ -452,11 +452,11 @@ class Repo:
         assert 200 <= r.status_code < 300, r.json()
         wait_for_hook()
 
-    def make_commit(self, ref, message, author, committer=None, tree=None, changes=None):
+    def make_commit(self, ref, message, author, committer=None, tree=None):
         assert tree, "not supporting changes/updates"
         assert not (author or committer)
 
-        if ref is None:
+        if not ref: # None / []
             # apparently github refuses to create trees/commits in empty repos
             # using the regular API...
             [(path, contents)] = tree.items()
@@ -469,7 +469,11 @@ class Repo:
             assert 200 <= r.status_code < 300, r.json()
             return r.json()['commit']['sha']
 
-        parent = self.get_ref(ref)
+        if isinstance(ref, list):
+            refs = ref
+        else:
+            refs = [ref]
+        parents = [self.get_ref(r) for r in refs]
 
         r = self._session.post('https://api.github.com/repos/{}/git/trees'.format(self.name), json={
             'tree': [
@@ -481,7 +485,7 @@ class Repo:
         h = r.json()['sha']
 
         r = self._session.post('https://api.github.com/repos/{}/git/commits'.format(self.name), json={
-            'parents': [parent],
+            'parents': parents,
             'message': message,
             'tree': h,
 
@@ -490,8 +494,9 @@ class Repo:
 
         commit_sha = r.json()['sha']
 
-        if parent != ref:
-            self.update_ref(ref, commit_sha)
+        # if the first parent is an actual ref (rather than a hash) update it
+        if parents[0] != refs[0]:
+            self.update_ref(refs[0], commit_sha)
         else:
             wait_for_hook()
         return commit_sha
diff --git a/runbot_merge/tests/test_basic.py b/runbot_merge/tests/test_basic.py
index 9bded03a..0e5543cb 100644
--- a/runbot_merge/tests/test_basic.py
+++ b/runbot_merge/tests/test_basic.py
@@ -638,11 +638,9 @@ class TestMergeMethod:
 
         # create a dag (msg:str, parents:set) from the log
         staging = log_to_node(repo.log('heads/staging.master'))
-        # then compare to the dag version of the right graph (nb: parents is
-        # a frozenset otherwise can't put a node in a node as tuples are
-        # only hashable if their contents are)
-        nm2 = ('M2', frozenset([('M1', frozenset([('M0', frozenset())]))]))
-        nb1 = ('B1', frozenset([('B0', frozenset([nm2]))]))
+        # then compare to the dag version of the right graph
+        nm2 = node('M2', node('M1', node('M0')))
+        nb1 = node('B1', node('B0', nm2))
         expected = (
             'title\n\nbody\n\ncloses {}#{}'.format(repo.name, prx.number),
             frozenset([nm2, nb1])
@@ -654,19 +652,125 @@ class TestMergeMethod:
 
     @pytest.mark.skip(reason="what do if the PR contains merge commits???")
     def test_pr_contains_merges(self, repo, env):
-        """
-        """
+        pass
 
     def test_pr_unrebase(self, repo, env):
-        """ should be possible to flag a PR as regular-merged
+        """ should be possible to flag a PR as regular-merged, regardless of
+        its commits count
+
+        M      M<--+
+        ^      ^   |
+        |  ->  |   C0
+        +      |   ^
+        C0     +   |
+               gib-+
         """
-        pytest.skip("todo")
+        m = repo.make_commit(None, "M", None, tree={'a': 'a'})
+        repo.make_ref('heads/master', m)
+
+        c0 = repo.make_commit(m, 'C0', None, tree={'a': 'b'})
+        prx = repo.make_pr("gibberish", "blahblah", target='master', ctid=c0, user='user')
+        env['runbot_merge.project']._check_progress()
+
+        repo.post_status(prx.head, 'success', 'legal/cla')
+        repo.post_status(prx.head, 'success', 'ci/runbot')
+        prx.post_comment('hansen r+ rebase-', 'reviewer')
+        env['runbot_merge.project']._check_progress()
+
+        repo.post_status('heads/staging.master', 'success', 'ci/runbot')
+        repo.post_status('heads/staging.master', 'success', 'legal/cla')
+        env['runbot_merge.project']._check_progress()
+
+        master = repo.commit('heads/master')
+        assert master.parents == [m, prx.head], \
+            "master's parents should be the old master & the PR head"
+
+        m = node('M')
+        c0 = node('C0', m)
+        expected = node('gibberish\n\nblahblah\n\ncloses {}#{}'.format(repo.name, prx.number), m, c0)
+        assert log_to_node(repo.log('heads/master')), expected
 
     def test_pr_mergehead(self, repo, env):
         """ if the head of the PR is a merge commit and one of the parents is
         in the target, replicate the merge commit instead of merging
+
+        rankdir="BT"
+        M2 -> M1
+        C0 -> M1
+        C1 -> C0
+        C1 -> M2
+
+        C1 [label = "\\N / MERGE"]
         """
-        pytest.skip("todo")
+        m1 = repo.make_commit(None, "M1", None, tree={'a': '0'})
+        m2 = repo.make_commit(m1, "M2", None, tree={'a': '1'})
+        repo.make_ref('heads/master', m2)
+
+        c0 = repo.make_commit(m1, 'C0', None, tree={'a': '0', 'b': '2'})
+        c1 = repo.make_commit([c0, m2], 'C1', None, tree={'a': '1', 'b': '2'})
+        prx = repo.make_pr("T", "TT", target='master', ctid=c1, user='user')
+        env['runbot_merge.project']._check_progress()
+
+        repo.post_status(prx.head, 'success', 'legal/cla')
+        repo.post_status(prx.head, 'success', 'ci/runbot')
+        prx.post_comment('hansen r+ rebase-', 'reviewer')
+        env['runbot_merge.project']._check_progress()
+
+        repo.post_status('heads/staging.master', 'success', 'ci/runbot')
+        repo.post_status('heads/staging.master', 'success', 'legal/cla')
+        env['runbot_merge.project']._check_progress()
+
+        master = repo.commit('heads/master')
+        assert master.parents == [m2, c0]
+        m1 = node('M1')
+        expected = node('C1', node('C0', m1), node('M2', m1))
+        assert log_to_node(repo.log('heads/master')), expected
+
+    def test_pr_mergehead_nonmember(self, repo, env):
+        """ if the head of the PR is a merge commit but none of the parents is
+        in the target, merge normally
+
+        rankdir="BT"
+        M2 -> M1
+        B0 -> M1
+        C0 -> M1
+        C1 -> C0
+        C1 -> B0
+
+        MERGE -> M2
+        MERGE -> C1
+        """
+        m1 = repo.make_commit(None, "M1", None, tree={'a': '0'})
+        m2 = repo.make_commit(m1, "M2", None, tree={'a': '1'})
+        repo.make_ref('heads/master', m2)
+
+        b0 = repo.make_commit(m1, 'B0', None, tree={'a': '0', 'bb': 'bb'})
+
+        c0 = repo.make_commit(m1, 'C0', None, tree={'a': '0', 'b': '2'})
+        c1 = repo.make_commit([c0, b0], 'C1', None, tree={'a': '0', 'b': '2', 'bb': 'bb'})
+        prx = repo.make_pr("T", "TT", target='master', ctid=c1, user='user')
+        env['runbot_merge.project']._check_progress()
+
+        repo.post_status(prx.head, 'success', 'legal/cla')
+        repo.post_status(prx.head, 'success', 'ci/runbot')
+        prx.post_comment('hansen r+ rebase-', 'reviewer')
+        env['runbot_merge.project']._check_progress()
+
+        repo.post_status('heads/staging.master', 'success', 'ci/runbot')
+        repo.post_status('heads/staging.master', 'success', 'legal/cla')
+        env['runbot_merge.project']._check_progress()
+
+        master = repo.commit('heads/master')
+        assert master.parents == [m2, c1]
+        assert repo.read_tree(master) == {'a': b'1', 'b': b'2', 'bb': b'bb'}
+
+        m1 = node('M1')
+        expected = node(
+            'T\n\nTT\n\ncloses {}#{}'.format(repo.name, prx.number),
+            node('M2', m1),
+            node('C1', node('C0', m1), node('B0', m1))
+        )
+        assert log_to_node(repo.log('heads/master')), expected
 
     @pytest.mark.xfail(reason="removed support for squash+ command")
     def test_force_squash_merge(self, repo, env):
@@ -1323,6 +1427,9 @@ class TestUnknownPR:
         env['runbot_merge.project']._check_progress()
         assert pr.staging_id
 
+def node(name, *children):
+    assert type(name) is str
+    return name, frozenset(children)
 def log_to_node(log):
     log = list(log)
     nodes = {}
diff --git a/runbot_merge/tests/test_multirepo.py b/runbot_merge/tests/test_multirepo.py
index b06a704e..8f9a20e4 100644
--- a/runbot_merge/tests/test_multirepo.py
+++ b/runbot_merge/tests/test_multirepo.py
@@ -202,6 +202,7 @@ def test_ff_fail(env, project, repo_a, repo_b):
 
     # add second commit blocking FF
     cn = repo_b.make_commit('heads/master', 'second', None, tree={'a': 'b_0', 'b': 'other'})
+    assert repo_b.commit('heads/master').id == cn
 
     repo_a.post_status('heads/staging.master', 'success', 'ci/runbot')
     repo_a.post_status('heads/staging.master', 'success', 'legal/cla')